Persistent, antigen-specific, therapeutic antitumor immunity by dendritic cells genetically modified with an adenoviral vector to express a model tumor antigen

Dendritic cell-based cancer immunotherapy for pancreatic cancer

Pancreatic cancer (PC) is a lethal disease and remains one of the most resistant cancers to traditional therapies. New therapeutic modalities are urgently needed, particularly immunotherapy, which has shown promise in numerous animal model studies. Dendritic cell (DC)-based immunotherapy has been used in clinical trials for various cancers, including PC, because DCs are the most potent antigen-presenting cell (APC), which are capable of priming naive T cells and stimulating memory T cells to generate antigen-specific responses. In this paper, we review the preclinical and clinical efforts towards the application of DCs for PC.

Measles virus glycoprotein-pseudotyped lentiviral vectors are highly superior to vesicular stomatitis virus G pseudotypes for genetic modification of monocyte-derived dendritic cells

Dendritic cells (DCs) are potent antigen-presenting cells capable of promoting or regulating innate and adaptive immune responses against non-self antigens. To better understand the DC biology or to use them for immune intervention, a tremendous effort has been made to improve gene transfer in these cells. Lentiviral vectors (LVs) have conferred a huge advantage in that they can transduce nondividing cells such as human monocyte-derived DCs (MDDCs) but required high amounts of viral particles and/or accessory proteins such as Vpx or Vpr to achieve sufficient transduction rates. As a consequence, these LVs have been shown to cause dramatic functional modifications, such as the activation or maturation of transduced MDDCs. Taking advantage of new pseudotyped LVs, i.e., with envelope glycoproteins from the measles virus (MV), we demonstrate that MDDCs are transduced very efficiently with these new LVs compared to the classically used vesicular stomatitis virus G-pseudotyped LVs and thus allowed to achieve high transduction rates at relatively low multiplicities of infection. Moreover, in this experimental setting, no activation or maturation markers were upregulated, while MV-LV-transduced cells remained able to mature after an appropriate Toll-like receptor stimulation. We then demonstrate that our MV-pseudotyped LVs use DC-SIGN, CD46, and CD150/SLAM as receptors to transduce MDDCs. Altogether, our results show that MV-pseudotyped LVs provide the most accurate and simple viral method for efficiently transferring genes into MDDCs without affecting their activation and/or maturation status.

Pre-clinical characterization of GMP grade CCL21-gene modified dendritic cells for application in a phase I trial in non-small cell lung cancer

Background

Our previous studies have demonstrated that transduction of human dendritic cells (DC) with adenovirus encoding secondary lymphoid chemokine, CCL21, led to secretion of biologically active CCL21 without altering DC phenotype or viability. In addition, intratumoral injections of CCL21-transduced DC into established murine lung tumors resulted in complete regression and protective anti-tumor immunity. These results have provided the rationale to generate a clinical grade adenoviral vector encoding CCL-21 for ex vivo transduction of human DC in order to assess intratumoral administration in late stage human lung cancer.

Methods

In the current study, human monocyte-derived DC were differentiated by exposure to GM-CSF and IL-4 from cryopreserved mononuclear cells obtained from healthy volunteers. Transduction with clinical grade adenoviral vector encoding CCL21 (1167 viral particles per cell) resulted in secretion of CCL21 protein.

Results

CCL21 protein production from transduced DC was detected in supernatants (24–72 hours, 3.5–6.7 ng/4–5 × 10⁶ cells). DC transduced with the clinical grade adenoviral vector were > 88% viable (n = 16), conserved their phenotype and maintained integral biological activities including dextran uptake, production of immunostimulatory cytokines/chemokines and antigen presentation. Furthermore, supernatant from CCL21-DC induced the chemotaxis of T2 cells in vitro.

Conclusion

Viable and biologically active clinical grade CCL21 gene-modified DC can be generated from cryopreserved PBMC.

Engineered lentivector targeting of dendritic cells for in vivo immunization

We report a method of inducing antigen production in dendritic cells by in vivo targeting with lentiviral vectors that specifically bind to the dendritic cell-surface protein DC-SIGN. To target dendritic cells, we enveloped the lentivector with a viral glycoprotein from Sindbis virus engineered to be DC-SIGN-specific. In vitro, this lentivector specifically transduced dendritic cells and induced dendritic cell maturation. A high frequency (up to 12%) of ovalbumin (OVA)-specific CD8(+) T cells and a significant antibody response were observed 2 weeks after injection of a targeted lentiviral vector encoding an OVA transgene into naive mice. This approach also protected against the growth of OVA-expressing E.G7 tumors and induced regression of established tumors. Thus, lentiviral vectors targeting dendritic cells provide a simple method of producing effective immunity and may provide an alternative route for immunization with protein antigens.

Patient-derived dendritic cells transduced with an a-fetoprotein-encoding adenovirus and co-cultured with autologous cytokine-induced lymphocytes induce a specific and strong immune response against hepatocellular carcinoma cells

BACKGROUND/AIMS

Breaking immunologic tolerance towards the hepatocellular carcinoma (HCC)-associated alpha-fetoprotein (AFP) antigen is possible. The use of this potential for the treatment of immunocompromised HCC patients is limited. In this study, we analyzed whether dendritic cells (DCs) from HCC patients transduced with a human AFP (hAFP)-expressing adenovirus and co-cultured with cytokine-induced killer (CIK) cells can induce a strong specific immune response against HCC-cells.

METHODS

An hAFP-encoding adenovirus (Ad-hAFP) was generated. DCs from healthy donors or patients were transduced at a very high efficacy. Afterwards, DCs were co-cultured with autologous CIK-cells, and their ability to lyse HCC-cells was analyzed.

RESULTS

AFP-transduced DCs stimulated CIK cells strongly to lyse about 70% of AFP-expressing HCC cells. Cytotoxicity was significantly higher when lymphocytes were co-cultured with Ad-hAFP-transduced DCs than with Ad-mock-transduced DCs, indicating an AFP-specific immune response. More interestingly, CIK cells from patients with AFP-positive HCC could be stimulated to lyse AFP-expressing HCC cells as effectively as CIK cells from healthy individuals and stronger than CIK cells from patients without AFP-expressing HCC.

CONCLUSIONS

The data demonstrate that patient-derived DCs that were transduced with an AFP-expressing adenovirus and co-cultured with autologous CIK cells induce an AFP-specific, strong immune response against HCC cells. Therefore, this approach may have a potential for an adoptive and/or DC-based immunotherapy for HCC patients.

Therapeutic vaccination against murine lymphoma by intratumoral injection of naive dendritic cells

Dendritic cells are potent antigen-presenting cells that can induce both immune responses and tolerance depending on their state of activation. Immunologic tolerance to established tumors is a major impediment for the development of effective cancer immunotherapy. Dendritic cells may be deficient in number or in function at the tumor site. To address this problem, we evaluated the ability of immature naïve dendritic cells to induce an antitumor immune response when injected directly into a murine B-cell lymphoma. Mice with advanced transplanted syngeneic tumor were given intratumoral injections of bone marrow-derived dendritic cells. Intratumoral dendritic cell injection alone had no antitumor effect. Systemic chemotherapy alone resulted in only transient tumor regression. However, the intratumoral injection of dendritic cells after chemotherapy led to complete, long-term tumor regression in the majority of treated mice. This dendritic cell-mediated antitumor effect was systemic, resulting in simultaneous elimination of the tumor at second uninjected sites. In addition, it resulted in long-term memory with resistance to tumor rechallenge. Both CD4+ and CD8+ T cells are necessary for the antitumor effect. Furthermore, tumors that occasionally recurred in mice with initial complete tumor regression could be retreated by the same combined chemoimmunotherapy approach. These results show that immunotherapy can succeed in the setting of advanced lymphoma if dendritic cells are restored and loaded with tumor antigens in situ at a single tumor site.

Dendritic cells transduced with tumor-associated antigen gene elicit potent therapeutic antitumor immunity: comparison with immunodominant peptide-pulsed DCs

Several studies have shown that vaccine therapy using dendritic cells (DCs) pulsed with specific tumor antigen peptides can effectively induce antitumor immunity. Peptide-pulsed DC therapy is reported to be effective against melanoma, while it is still not sufficient to show the antitumor therapeutic effect against epithelial solid tumors such as gastrointestinal malignancies. Recently, it has been reported that vaccine therapy using DCs transduced with a surrogate tumor antigen gene can elicit a potent therapeutic antitumor immunity. In this study, we investigated the efficacy of vaccine therapy using DCs transduced with the natural tumor antigen in comparison with peptide-pulsed DCs. DCs derived from murine bone marrow were adenovirally transduced with murine endogenous tumor antigen gp70 gene, which is expressed in CT26 cells, or DCs were pulsed with the immunodominant peptide AH-1 derived from gp70. We compared these two cancer vaccines in terms of induction of antigen-specific cytotoxic T lymphocyte (CTL) responses, CD4+ T cell response against tumor cells, migratory capacity of DCs and therapeutic immunity in vivo. The cytotoxic activity of splenocytes against CT26 and Meth-A pulsed with AH-1 in mice immunized with gp70 gene-transduced DCs was higher than that with AH-1-pulsed DCs. CD4+ T cells induced from mice immunized with gp70 gene-transduced DCs produced higher levels of IFN-gamma by stimulation with CT26 than those from mice immunized with AH-1-pulsed DCs (p < 0.0001), and it was suggested that DCs transduced with tumor-associated antigen (TAA) gene induced tumor-specific CD4+ T cells, and those CD4+ T cells played a critical role in the priming phase of the CD8+ T cell response for the induction of CD8+ CTL. Furthermore, DCs adenovirally transduced with TAA gene showed an enhancement of expression of CC chemokine receptor 7 and improved the migratory capacity to draining lymph nodes. In subcutaneous models, the vaccination using gp70 gene-transduced DCs provided a remarkably higher therapeutic efficacy than that using AH-1-pulsed DCs. These results suggested that vaccine therapy using DCs adenovirally transduced with TAA gene can elicit potent antitumor immunity, and may be useful for clinical application.

An APC for every occasion: induction and expansion of human Ag-specific CD4 and CD8 T cells using cellular and non-cellular APC

APC are used extensively to induce and expand Ag-specific T cells as well as to test their specificity and function. In the treatment of malignant and infectious diseases, APC are used to stimulate and expand Ag-specific T cells for adoptive transfer, or used directly in vivo to present Ag. The choice of APC to use depends on the particular application and on practical considerations, which include ease of production, availability, reproducibility and (for clinical use) established safety. The diversity of APC in use partly reflects the fact that no single technique of Ag presentation is ideal. For the clinician and laboratory worker alike the field can seem illogical and confusing. In this review we outline the functional requirements of APC for the induction of T cells, classify the APC in common use and describe their laboratory and clinical applications.

Modifying Adenoviral Vectors for Use as Gene-Based Cancer Vaccines

The past decade has produced significant advances in our understanding of antigen-presenting cells, tumor antigens, and other components of the immune response to cancer. Gene-based vaccination is emerging as one of the more promising approaches for loading dendritic cells (DC) with tumor-associated antigens. In this respect, it is proposed that adenoviral (AdV) vectors can deliver high antigen concentrations, promote effective processing and MHC expression, and stimulate potent cell-mediated immunity. While AdV vectors have performed well in pre-clinical vaccine models, their application to patient care has limitations. The in vivo administration of AdV vectors is associated with both innate and adaptive host responses that result in tissue inflammation and injury, viral neutralization, and premature clearance of AdV-transduced cells. A variety of strategies have been developed to address these limitations. The ideal vaccine would avoid vector-related immune responses, have relative specificity for transducing DC, and induce high levels of transgene expression. This review describes the range of host responses to AdV vaccines, identifies strategies to reduce viral recognition and enhance transgene antigen expression, and suggests future approaches to vector development and administration. There is every reason to believe that safer and more effective forms of AdV-based vaccines can be developed and applied to patient therapy.

Efficient Induction of CD8 T-Associated Immune Protection by Vaccination with mRNA Transfected Dendritic Cells

Dendritic cells are excellent targets for antigen-specific immune intervention. Here we attempted to introduce a CD8 T cell-dependent epitope into dendritic cells for presentation on major histocompatibility complex class I and induction of immunity. Murine bone-marrow-derived dendritic cells were subjected to electroporation with mRNA transcribed in vitro from a plasmid encoding lymphocytic choriomeningitis virus glycoprotein or enhanced green fluorescent protein under the control of a T7 promotor. The transfection efficiency of dendritic cells was 22 to 40%. Maturation was not inhibited by the electroporation. Dendritic cells electroporated with the appropriate antigen induced cell number-dependent in vitro proliferation in CD8 T cells expressing a transgenic receptor recognizing the 33 to 41 sequence of lymphocytic choriomeningitis virus glycoprotein in association with H-2Kb/Db, indicating correct synthesis, processing, and presentation of the epitope. Naive C57BL/6 mice vaccinated with electroporated dendritic cells and challenged with lymphocytic choriomeningitis virus were protected. Vaccination induced epitope-specific T cells as assessed by tetramer staining in blood and spleen. These results indicate that targeting dendritic cells with antigen-encoding mRNA can induce antigen-specific CD8 T cell responses as well as protective anti-viral immunity in vivo. Targeting dendritic cells with antigen-encoding mRNA may find wider application for immune intervention in disorders such as autoimmunity and cancer.

Priming of T cells with Ad-transduced DC followed by expansion with peptide-pulsed DC significantly enhances the induction of tumor-specific CD8+ T cells: implications for an efficient vaccination strategy

In recent years, vaccination strategies using antigen-presenting cells (APC) have been under investigation. Antigen delivery using genetic immunization through ex vivo transduction of dendritic cells (DC) is supposed to enhance the induction of antitumor responses in humans by activating a broad range of peptide-specific CD8+ T cells. In this study, we compared the potential of adenoviral (Ad)-transduced versus peptide-pulsed DC to induce melanoma-antigen (Ag)-specific T-cell responses in vitro. Whereas gp100-peptide-pulsed DC induced long-lasting specific CD8+ T-cell responses against single peptides, Ad-transduced DC induced broad and strong, specific immunity against various peptides of the gp100-Ag. Surprisingly, several restimulations led to decreasing gp100-specific and in parallel to increasing anti-adenoviral T-cell responses. Nevertheless, those anti-adenoviral T-cell responses provided an "adjuvant" effect by inducing an early release of high amounts of IL-2/IFN-gamma, therewith enhancing CTL induction in the initiation phase. Based on these data, we suggest a prime/boost vaccination strategy in melanoma patients--combining the use of Ad-DC and peptide-pulsed DC--to obtain efficient and long-term antitumor T-cell responses.

Helper-dependent adenoviral vectors efficiently express transgenes in human dendritic cells but still stimulate antiviral immune responses

Adenoviral (AdV) vectors can be used to transduce a wide range of human cells and tissues. However, pre-existing immunity to AdV, and enhancement of this immunity after repeated administration, limits their clinical application. This may be especially relevant when vectors are loaded into APCs. Helper-dependent AdV (Hd-AdV), in which viral coding regions are replaced by human stuffer DNA, offers a new approach for limiting antiviral responses. To evaluate their immunogenicity, human dendritic cells (DCs) were infected with either an Hd-AdV or a conventional replication-deficient E1-deleted AdV (E1-AdV) and were evaluated for their capacity to stimulate antiviral T cell responses. Hd-AdV proved to be 50- to 275-fold more effective than E1-AdV at expressing the lacZ transgene in human DCs. PCR demonstrated similar transduction efficiencies, but RT-PCR revealed much higher expression of transgene mRNA after transduction with Hd-AdV. Functionally, DCs transduced with Hd-AdV stimulated the proliferation of autologous T cells to the same level as DCs transduced with E1-AdV. Identical viral-specific T cell responder frequencies were observed and T cells stimulated with either type of AdV-transduced DC lysed viral-infected target cells. Disrupting transcription of vector-based genes had no effect on T cell activation, suggesting that responses against both vectors were directed against preformed components of the viral capsid. We conclude that Hd-AdV vectors can be used to obtain higher transgene expression in human DCs but that they still evoke a vector-related immune response similar to that generated by E1-AdV.

DNA-based immunotherapy: potential for treatment of chronic viral hepatitis?

Persistent HBV and HCV infection represent major causes of chronic liver disease with a high risk of progression to liver cirrhosis and hepatocellular carcinoma (HCC). Conventional protein-based vaccines are highly efficacious in preventing HBV infection; whereas in therapeutic settings with chronically infected patients, results have been disappointing. Prophylactic vaccination against HCV infection has not yet been achieved due to many impediments including frequent spontaneous mutations of the virus with escape from immune system control. Using animal models it has been demonstrated that DNA-based immunisation strategies may overcome this problem because of their potential to induce immunity against multiple viral epitopes. DNA-based vaccines mimic the effect of live attenuated viral vaccines, eliciting cell mediated immunity in addition to inducing humoral responses. Efficacy may further be improved by addition of DNA encoding immunomodulatory cytokines and more recently, direct genetic modulation of antigen-presenting cells, such as dendritic cells (DC), has been shown to increase antigen-specific immune responses. This review focuses on immunological aspects of chronic HBV and HCV infection and on the potential of DNA- and DC-based vaccines for the treatment of chronic viral hepatitis.

Efficient genetic modification of murine dendritic cells by electroporation with mRNA

Recently, human dendritic cells (DCs) pulsed with mRNA encoding a broad range of tumor antigens have proven to be potent activators of a primary anti-tumor-specific T-cell response in vitro. The aim of this study was to improve the mRNA pulsing of murine DC. Compared to a standard lipofection protocol and passive pulsing, electroporation was, in our hands, the most efficient method. The optimal conditions to electroporate murine bone marrow-derived DCs with mRNA were determined using enhanced green fluorescent protein and a truncated form of the nerve growth factor receptor. We could obtain high transfection efficiencies around 70-80% with a mean fluorescence intensity of 100-200. A maximal expression level was reached 3 hours after electroporation. A clear dose-response effect was seen depending on the amount of mRNA used. Importantly, the electroporation process did not affect the viability nor the allostimulatory capacity or phenotype of the DC. To study the capacity of mRNA-electroporated DCs to present antigen in the context of MHC classes I and II, we made use of chimeric constructs of ovalbumin. The dose-dependent response effect and the duration of presentation were also determined. Together, these results demonstrate that mRNA electroporation is a useful method to generate genetically modified murine DC, which can be used for preclinical studies testing immunotherapeutic approaches.

Gene therapy for pancreatic cancer

Gene transfer technology has the potential to revolutionize cancer treatment. Developments in molecular biology, genetics, genomics, stem cell technology, virology, bioengineering, and immunology are accelerating the pace of innovation and movement from the laboratory bench to the clinical arena. Pancreatic adenocarcinoma, with its particularly poor prognosis and lack of effective traditional therapy for most patients, is an area where gene transfer and immunotherapy have a maximal opportunity to demonstrate efficacy. In this review, we have discussed current preclinical and clinical investigation of gene transfer technology for pancreatic cancer. We have emphasized that the many strategies under investigation for cancer gene therapy can be classified into two major categories. The first category of therapies rely on the transduction of cells other than tumor cells, or the limited transduction of tumor tissue. These therapies, which do not require efficient gene transfer, generally lead to systemic biological effects (e.g., systemic antitumor immunity, inhibition of tumor angiogenesis, etc) and therefore the effects of limited gene transfer are biologically "amplified." The second category of gene transfer strategies requires the delivery of therapeutic genetic material to all or most tumor cells. While these elegant approaches are based on state-of-the-art advances in our understanding of the molecular biology of cancer, they suffer from the current inadequacies of gene transfer technology. At least in the short term, it is very likely that success in pancreatic cancer gene therapy will involve therapies that require only the limited transduction of cells. The time-worn surgical maxim, "Do what's easy first," certainly applies here.